1. Field of the Invention
The present invention relates to an instrument used for detecting contamination of the surface of a semiconductor wafer and to technology associated therewith, and more particularly, to an instrument suitable for detecting contaminants adhering to a wafer surface by means of the water-extracting technique.
2. Background Art
Contaminants adhering to a wafer surface are responsible for deterioration of the yield, performance, and reliability of a semiconductor device. Processes for manufacturing a semiconductor device include a number of cleaning steps. In spite of those cleaning steps, a wafer surface may be contaminated with particles, metal, various ions, or organic substances. In the event of a wafer surface being contaminated, immediate investigation of the source and cause of contamination is required for maintaining a high degree of cleanliness of semiconductor manufacturing processes. The importance of high-degree cleanliness grows increasingly in association with an increase in the density and integration of a semiconductor device.
Contamination of a wafer surface is usually determined by means of extracting. contaminants adhering to a wafer surface, through use of a specifically-designed solvent. The thus-extracted solution is subjected to qualitative/quantitative analysis by use of an analyzer [for example, ICP-MS (High-Frequency Inductively-Coupled Plasma Mass Analyzing System)].
According to the conventional technique for extracting contaminants to be delivered to analyzing processes, a wafer is put in a film pack for extracting a hot-water bag, and pure water is poured into the film pack. The wafer is left in its present form in a thermostatic chamber while being immersed in pure water within the film pack, to thereby extract the contaminants adhering to the wafer surface.
In the course of processes for manufacturing a semiconductor device, handling of an upper surface (a mirror-surface side) of a wafer completely differs from handling of an underside surface of the wafer. Further, the required cleanliness of an upper surface also greatly differs from that of an underside surface. Naturally, the state of contamination of the upper surface of the wafer greatly differs from that of the underside of the same. For this reason, contamination of the upper surface and contamination of the underside are preferably determined on an individual basis. The conventional extraction method involves a chance of the substances (contaminants) extracted from the upper surface and the substances extracted from the underside being mixed during the course of extraction processes, with the result that determination of contamination of solely the upper surface of a wafer has been infeasible.
To enable determination of contamination of a single side of a wafer, there, is used an extraction system which can extract contaminants from a respective side of a wafer by means of adding pure water to the surface of the wafer situated horizontally and vibrating the wafer. Although the extraction system enables extraction of contaminants from a single side of a wafer, the system can extract contaminants from solely either side of the wafer by way of a single determination operation. In a case where contamination of either side,of a wafer is desired to be determined, there must be prepared two wafers; i.e., one to be used for extracting contaminants from the upper surface of a wafer, and the other one to be used for extracting contaminants from the underside of the wafer.
Further, contaminants cannot be accurately determined unless contaminants are removed from the extraction system. For this reason, the extraction system must be cleaned every extraction operation. Thus, extraction of contaminants from either side of a wafer through use of such a extraction system involves consumption of much time and labor.
In association with a recent tendency toward an increase in the diameter of a wafer, predetermined areas on the same side of a wafer must be controlled in manners which differ from area to area. therefore, demand exists for not only attaining uniform cleanliness of solely either side of a wafer but also for attaining different degrees of cleanliness in a plurality of respective areas on the same surface. Increasing demand exists for a necessity for measuring contamination of a single surface as well as contamination of limited areas within a single surface. Any of the foregoing methods encounters difficulty in measuring contamination of limited areas on a wafer surface.
The present invention has been conceived in consideration of the above-described drawback of the background art and is aimed at providing an instrument capable of immediately and accurately extracting contaminants from solely either side of a wafer surface or from a certain area on the wafer surface.
As a result of considerable studies conducted by the inventors in order to solve the above-described drawback of the background art, the inventors have conceived an instrument suitable for independently and simultaneously measuring contaminants from the upper surface and underside of a wafer to be inspected, by means of enclosing certain areas on the upper surface and underside of the wafer independently, and feeding extraction solvent to the thus-enclosed areas independently. Thus, the inventors have completed the present invention.
To this end, a wafer to be inspected is held in a disposable film pack, and extraction solvent is fed into and drawn from the film pack, thereby eliminating a necessity for cleaning the extraction instrument every measurement operation. As a result, the clean state of the extraction instrument can be maintained, and an extraction operation can be made simple.
The instrument for measuring contamination of a wafer surface embodying the aforementioned idea is essentially materialized as follows:
(1) An instrument to be used for extracting contaminants from a wafer surface to be inspected, comprising:
a pair of wafer holding members which are provided opposite each other and hold the wafer from respective sides;
a curved protruding member provided on a surface of at least one of the wafer holding members, the surface being faced with the wafer, so as to cover a certain portion of the wafer surface while ensuring a predetermined entrance space; and
solvent to be used for extraction being reserved in a space formed between the wafer holding member and the wafer as a result of presence of the curved protruding member.
(2) Preferably, a support member for supporting the lower edge of the wafer to be inspected is provided on a lower portion of the wafer holding member, to thereby position the wafer.
(3) Preferably, the curved protruding member is a cord-like member.
(4) Preferably, the curve of the curved protruding member assumes a circular geometry.
(5) Preferably, an instrument set for measuring contamination of a wafer comprises the instrument for measuring contamination of a wafer surface, and a disposable bag for holding the wafer. The wafer held in the bag is held from both side thereof.
(6) Preferably, a portion of the disposable bag to be enclosed by the curved protruding member and a portion of the same corresponding to the predetermined entrances bulge particularly.
In a case where such a bag is used, storage of solvent to be used for extracting contaminants becomes comparatively easy. Therefore, a disposable bag is suitable for measurement.
The present invention further includes the following method derived by generalization of use of the instrument according to the present invention.
(7) The present invention provides a method of measuring contaminants adhering to a wafer surface through extraction, the method comprising the steps of:
enclosing a certain area on the upper surface of a wafer to be inspected independently of another certain area on the underside of the wafer; and
feeding and drawing extraction solvent to and from each of the enclosed areas independently, to thereby enable simultaneous and independent measurement of contaminants on the upper surface and underside of the wafer.
Simultaneous and independent extraction of contaminants on the upper surface and underside of a wafer is implemented for the first time by the present invention. Accordingly, the following method utilizing the foregoing method should be conceived as an invention significant to semiconductor manufacturing processes.
(8) The present invention also provides a method of manufacturing a semiconductor device, utilizing an inspection step in which extraction of contaminants adhering to the upper surface of a wafer and extraction of contaminants adhering to the underside of the wafer are carried out simultaneously and independently.
The expression xe2x80x9cutilizingxe2x80x9d is a broad concept including not only a case where the inspection step is incorporated into a round of processes for manufacturing a semiconductor device but also a case where the inspection step is used during the course of a series of processes for manufacturing a semiconductor device.
More specifically, the following instrument for measuring contamination of a wafer surface corresponds to the instrument according to the present invention.
(9) An instrument to be used for extracting contaminants from the surface of a wafer to be inspected, comprising:
a pair of wafer holding members capable of holding a wafer held in an impermeable bag;
fixing members for fixing the paired holding members while the holding members are brought opposite each other; and
a surrounding member provided on a surface of at least one of the wafer holding members, the surface being faced with the wafer, so as to enclose a certain area on the surface of the wafer.
(10) Preferably, a support member for supporting the lower edge of the wafer to be inspected is provided on a lower portion of at least one of the wafer holding members, to thereby position the wafer.
(11) Preferably, the surrounding member is a cord-like member.
(12) Preferably, the surrounding member is a curved protruding member having an entrance.
(13) Preferably, the curved of the curved protruding member assumes a circular geometry.
(14) Preferably, an instrument set for measuring contamination of a wafer comprises the instrument for measuring contamination of a wafer surface, and an impermeable bag for holding the wafer. The wafer held in the bag is held from one side thereof.
(15) Preferably, a portion of the impermeable bag to be enclosed by the curved protruding member and a portion of the same corresponding to the predetermined entrances bulge particularly.
The present invention further includes the following method derived by generalization of use of the instrument according to the present invention.
(16) The present invention provides a method of measuring contaminants adhering to a wafer surface through extraction, the method comprising the steps of:
holding a wafer to be inspected into an impermeable bag;
enclosing a certain area on the upper surface of the wafer independently of another certain area on the underside of the wafer; and
feeding and drawing extraction solvent to and from each of the enclosed areas independently, to thereby enable simultaneous and independent measurement of contaminants on the upper surface and underside of the wafer.
(17) The present invention also provides a method of manufacturing a semiconductor device, utilizing an inspection step in which extraction of contaminants adhering to the upper surface of a wafer to be inspected held in an impermeable bag and extraction of contaminants adhering to the underside of the wafer are carried out simultaneously and independently.
(18) The present invention also provides a method of measuring contaminants adhering to a wafer surface through extraction, the method comprising the steps of:
holding a wafer to be inspected in an impermeable bag;
enclosing a certain area on the surface of the wafer; and
feeding and drawing extraction solvent to and from the inside or outside of the enclosed area, to thereby measure the distribution of contaminants on the wafer surface.
(19) The present invention also provides a method of manufacturing a semiconductor device, utilizing an inspection step in which contaminants are extracted from a certain area on the surface of a wafer, the wafer being an object of inspection and held in an impermeable bag, to thereby enable determination of contaminants in a certain range of the wafer surface.
(20) Preferably, the pair of holding members are identical in shape, each assuming a rectangular parallelepiped geometry. Further, the fixing members are preferably clamping members for clamping the pair of holding members in a paired manner. The clamping members fix three sides of the paired rectangular-parallelepiped holding members.
(21) Preferably, the clamping members are fitted around the paired rectangular-parallelepiped holding members in a sliding manner.
Preferably, a groove for guiding a slide of the clamping members is formed in each of the paired rectangular-parallelepiped holding members.
(22) Preferably, the fixing members are formed from a pair of magnets which are respectively provided on the paired holding members and attract each other. The paired holding members are fixed on the surface of the wafer under the attraction force of the magnets.
In order to enable measurement of contaminants without fail, the present invention provides features such as those provided below.
(23) Preferably, the method of measuring contamination of a wafer surface and the method of manufacturing a semiconductor device, which are set forth each comprise a step of exposing the wafer surface to UV radiation. As a result of exposure of a wafer surface to UV radiation, inorganic atoms (such as chlorine atoms, sulfur atoms, or like atoms) and inorganic atom groups (sulfur groups, nitrate groups, or like atomic groups) are dissociated in the form of ions (for example, Fxe2x88x92, Clxe2x88x92, S2xe2x88x92, SO42xe2x88x92, NO3xe2x88x92, PO43xe2x88x92). Measurement of contaminants can be carried out without fail by means of extraction of such dissociated ions.
A wafer is usually exposed to UV radiation before measurement of contaminants on the surface of the wafer. However, during the course of measurement of contaminants of the wafer surface, the wafer is taken out and exposed to UV radiation, as required. Subsequently, the wafer may again be subjected to measurement of contaminants.
Preferably, a wafer can be exposed to UV radiation through use of ordinary UV radiation means, such as a UV lamp to which a mercury lamp is applied.
(24) Preferably, any one of the instrument sets set forth includes use of a quartz Petri dish for holding a wafer. A quartz Petri dish can be formed from the same material as that of a quartz cell to be used for measuring; for example, one exhibiting a ultraviolet absorption spectrum. Use of such a material can avoid a problem of the intensity of UV radiation being weakened by absorption of excessive absorption of UV radiation by a container or a problem of a measurement result being adversely affected by decomposition of a container through UV radiation.
(25) Preferably, the instrument employs a wafer having exposed to UV radiation as a wafer to be inspected. More specifically, any of the instruments set forth may use a wafer which has been exposed to UV radiation. As a result, ions, such as Clxe2x88x92 or NO3xe2x88x92, dissociated from organic substances through UV radiation are detected, to thereby enable more accurate measurement of inorganic substances.
Measurement of contaminants which is performed without fail through UV radiation can be generalized as follows:
(26) A method of measuring contaminants by extraction of contaminants adhering to the surface of a wafer to be inspected, the method including
a step of irradiating the surface of the wafer with an electromagnetic wave of predetermined wavelength responsive to the characteristics of the contaminants. The expression xe2x80x9celectromagnetic wavexe2x80x9d means UV radiation, electrons, or another suitable electromagnetic wave, according to the type of a substance presumed to be a contaminant.
[Definitions of Expressions]
A wafer to be inspected includes not only a silicon wafer but also all wafers, such as wafers of compound semiconductors, which can be used as a substrate of an electronic component, such as a CPU or memory. In the specification, either side of a wafer is referred to as a xe2x80x9csurface.xe2x80x9d In the case of a wafer whose one side is mirror polished, the mirror-polished surface of the wafer is referred to as an xe2x80x9cupper surface,xe2x80x9d and the other surface of the wafer is referred to as an xe2x80x9cunderside.xe2x80x9d In the case of a wafer whose both sides are mirror polished, the surface of the wafer particularly desired to be inspected (in general, the surface of the wafer which is subjected to wafer processing such as thin-film formation and etching and is to be subjected to more accurate mirror polishing than the other surface) is referred to as an xe2x80x9cupper surface.xe2x80x9d Further, the expression xe2x80x9ccontaminantxe2x80x9d refers to a substance which is to be detected as a result of extraction. The expression xe2x80x9csurfacexe2x80x9d used in connection with extraction signifies an area which may contain extractable contaminants.
The holding members employed in the present invention may be formed from a naturally-occurring substance such as metal or wood or an artificial substance such as a chemical substance, so long as the holding members possess sufficient rigidity so as to prevent leakage of extraction solvent, which would otherwise be caused when the holding members are deformed as a result of external force being applied to the holding members in order to maintain the holding members in an opposing state. From the viewpoint of ease of processing, a plastic member, such as polyacetal, acrylic resin, polyethylene terephthalate, or polypropylene, is desirable.
The xe2x80x9cstopping membersxe2x80x9d used in the present invention signify members capable of fixing the pair of holding members in an opposing state. As an example, there may be employed a stopper for enclosing the outer periphery of the holding members, a member having a structure for fixing the holding members through use of screws, or a member for fixing the holding members by way of a wafer as a result of attraction of magnets provided on the respective holding members.
The expression xe2x80x9cenclosing a certain area on the wafer surfacexe2x80x9d signifies that a predetermined area on a wafer surface desired to be measured or a predetermined area on a wafer surface desired to be excluded from objects of measurement is enclosed. The position and range of a certain area can be determined in correspondence with a predetermined area on the wafer surface requiring measurement. Further, the expression xe2x80x9ccertain areaxe2x80x9d signifies a certain area on a wafer surface isolated from the other area, regardless of whether the certain area is on the upper surface or underside of the wafer. For instance, xe2x80x9ccertain areaxe2x80x9d corresponds to the center, edge, or a portion of the center of a wafer surface.
The expression xe2x80x9ccurvedxe2x80x9d signifies a geometry comprising an entrance and a portion which is continued from the entrance and becomes wider as it departs from the entrance. Any geometry may be employed, so long as the geometry satisfies the requirements set forth. For instance, there may be employed a figure having a curved interior (having no angular portions) or a rectangular interior (angular interior), when viewed from above.
The xe2x80x9cprotruding memberxe2x80x9d may be provided on either of the paired wafer holding members or each of the paired wafer holding members. In a case where a protruding member is provided on each of the paired wafer holding members, contamination of the upper surface and underside of a wafer can be measured simultaneously. If a wafer to be inspected is sandwiched between the paired wafer holding members, the protruding members are preferably positioned so as to pair with and oppose each other. The paired xe2x80x9cprotruding membersxe2x80x9d may be slightly offset within a range in which the wafer is not damaged or fractured.
The protruding members may preferably be formed from chemically inactive rubber material or plastic material; for example, polytetrafluoroethylene. The protruding member may be formed into a predetermined contour, by means of hollowing planar material. In a case where the protruding member assumes a rope shape or a circumferential shape, an O-ring may be employed. For example, in a case where the protruding member is formed into a curved shape, the curved protruding member may be formed by means of hollowing a portion of planar material. In addition, in a case where the curved protruding member assumes a rope shape or a circular shape, there may be employed a member which is formed by cutting or breaking a portion of an O-ring, to thereby form an entrance. Further, the wafer holding member may be formed from a material different from that of the curved protruding member, or the wafer holding member and the curved protruding member may be formed from the same material. Moreover, the wafer holding member and the curved protruding member may be formed integrally.
The surface of the protruding member, which surface is to be brought into contact with a wafer, must be sufficiently smooth. The surface is required to exhibit smoothness such that solvent does not leak from a contact area when the protruding member is brought into pressing contact with a wafer at a predetermined pressure.
Measurement of contaminants includes qualitative measurement (i.e., the type""s of detected ions) and quantitative measurement (i.e., the concentration of detected contaminants).
Preferably, according to the present invention, a plurality of instruments are stacked, to thereby enable simultaneous measurement of a plurality of wafers. Preferably, under surfaces of two wafers (or upper surfaces of two wafers in some cases) are brought into contact, to thereby enable simultaneous measurement of two upper surfaces (or two undersides in some cases).
The impermeable bag used with the instrument corresponds to a bag which permits permeation of extraction solvent to be fed into the bag. A person skilled in the art may select any bag in accordance with the property of solvent to be fed into the bag, as required. For instance, a commercially-available polyvinyl bag may be employed. In a case where a disposable bag is used, a step of cleaning the instrument can be simplified.
A bulging portion may be formed by a method commonly used for molding of resin, such as a blowing. In a case where the curved protruding member assumes a rope shape or a circumferential shape (i.e., a shape corresponding to an O-ring whose portion is cut or broken for an entrance), a bulging portion is formed into a square-and-circle shape.
Usually, ultrapure hot water is used as solvent to be used for extracting contaminants. Solvent of 30 ml or thereabouts is used in accordance with the capacity of an existing measurement apparatus. In a case where ultrapure hot water is used as solvent, halide ions (fluoride ions, chloride ions, or like ions), pseudohalide ions (nitrate ions, sulfate ions, or like ions), or other negative ions (phosphate ions or like ions) can be detected. Further, a predetermined organic solvent corresponding to a contaminant desired to be detected may be employed as a solvent.